The present invention relates to a gas burner. It also relates to a cooking apparatus, such as a cooker or a slot-in cooking surface, using this gas burner
A fuel, for example a gas, which is injected into a burner enters a first zone where it is mixed with a first volume of combustive agent, for example air, in order to form a so-called xe2x80x9cprimaryxe2x80x9d mixture the richness of which exceeds its stoichiometric conditions. This mixture is then conducted into a convergent/divergent system which can in particular be a horizontal venturi, a radial venturi or a vertical venturi, and which we shall henceforth call xe2x80x9cventurixe2x80x9d. On leaving the venturi the primary mixture enters a recompression chamber surrounded by a peripheral wall of generally circular shape. Orifices are provided through this peripheral wall, orifices through which the primary mixture is ejected into the ambient milieu. The primary mixture is then diluted anew in a combustive agent, for example the ambient air, in order to more or less reach the stoichiometric conditions, that is to say to form a combustible mixture. When the combustible mixture is ignited, it is close to the outlet of the ejection orifices that the flames form.
These known burners have the disadvantage of having radially inside the ring of flames a central zone more or less devoid of heat exchange. This arrangement can be a major drawback when it is desired to cook a foodstuff evenly in a frying pan.
Two solutions have principally been adopted by the prior art to optimize the heat exchange surface, and thus the distribution of the heat at the base of the receptacle.
A first solution is to add at least one peripheral wall concentric to the first peripheral wall and situated in the central zone. However, this technique is expensive and more suited to large kitchens in industry or restaurants. This actually amounts to a practical doubling of all of the items of equipment of the burner, and assists the combustion of the primary mixture emerging from an internal peripheral wall, as this mixture cannot thin in the ambient air, which is not very abundant in the central zone.
A second solution, while retaining the generally circular shape of the burner, involves giving the peripheral wall a shape such that some of its parts extend more or less radially from the centre of the burner towards its periphery. This is the solution presented in documents NL 31636, U.S. Pat. No. 2257399 and U.S. Pat. No. 2320754. These documents are already old and date respectively from 1933, 1938 and 1938. The solutions which they disclose are suited to town gas, that is to say gas made in a factory and mainly used up until the middle of the XXth century. This town gas is essentially methane or hydrogen, that is to say a gas requiring a small supply of air in order to reach stoichiometric conditions. These techniques were abandoned with the use of richer gases such as propane and methane. The latter, having the greater calorific power, are also comprised of longer carbon chains the combustion of which requires a greater supply of air. For the forms of peripheral walls presented in the cited documents, there is little space available for each flame and some of them mingle, which is harmful to combustion.
Apart from the richness of the gases used, standards and customer requirements increase the difficulties encountered. Standards actually impose ever higher combustion rates. Moreover, customers seek cooking surfaces where the technical aspect is masked by the aesthetic aspect. For example, burners which have a low apparent height and a short distance between the base of a receptacle and the top of the cooking surface. Thus, combustion must be ever improved whereas the volume available for the dilution of the primary mixture with the ambient air is ever smaller.
The aim of the invention is thus to propose a burner capable of significantly increasing the heat exchange surface, satisfying the requirements of the standards in force, and the desires of present customers. The main condition for this is that the flames do not intermingle, that is to say that the primary mixture leaving an orifice of the peripheral wall has enough space to thin in a sufficient quantity of ambient air.
The following definitions will be used in this document. An ejection axis is an axis representing, in the two-dimensional figures on the attached sheets, a plane which is longitudinal and more or less median relative to the ejection orifices. An ejection axis is oriented and originates in the outlet of an ejection orifice and extends towards the outside of the burner. In the case of two converging ejection orifices, the convergence distance of an orifice is the distance separating the origin of the ejection axis of this orifice with the point of intersection from the ejection axes of the two orifices, which for example are neighbouring.
According to the invention, a non-circular burner satisfying the requirements already cited is principally characterized in that the orifices of the peripheral wall are realized such that the ejection axis of any first orifice diverges from the ejection axis of a second orifice closest to the first orifice. This definition does not stop another orifice next to the first orifice from converging with the first orifice, but then the convergence distance must guarantee sufficient diffusion.
According to another preferred feature of the invention, no ejection axis is directed towards a part of the peripheral wall, a part which could limit the available space. In order to optimize the heat exchange surface the peripheral wall can also be partly concave.
A burner according to the invention is intended in particular for domestic use. It is thus advantageous that it can be easily cleaned. To this end, the peripheral wall can be made so that it can be reached at any point of its periphery by at least one finger of one hand. On the other hand, to limit a catalysis phenomenon likely to degrade the enamel of a pan support intended to keep a receptacle above the burner, said peripheral wall can include neutralized segments in its parts close to the pan support. However, as the primary mixture ejected through one of the orifices mixes not at all or little with that ejected through a neighbouring orifice, it may be beneficial for a rapid ignition of the burner to have at least one of the ejection orifices connected to at least one neighbouring ejection orifice by a flame duct. A flame duct can for example connect two neighbouring orifices separated by a neutralized segment.
It is advantageous that the neutralized segments each correspond to a part of a concave zone. Another part of the concave zone can have orifices. Thus the desire to have flames in the zones close to the axis of the burner, but for these flames not to interfere with each other, is cleverly combined with the desire to have zones without flames in order to preserve the pan support.
To further improve combustion, it is advantageous to extend the venturi beyond at least one concave segment of the said peripheral wall.
A burner according to the invention can be an all-gas burner, i.e. one burning the rich gases, such as propane or butane, and the lean gases, such as methane, equally well. It can also be designed to obtain the spiral convection effect disclosed by document WO 96/01572, thanks to the same direction of inclination of the ejection axes relative to the zone of the peripheral wall from which they have respectively issued.
The invention also relates to a cooking apparatus using a burner having any one of the above characteristics. On such an apparatus using N burners, N being a whole number, the said N burners can be arranged along a line which is not necessarily rectilinear, on a working surface of the cooking apparatus such that the general shape of the peripheral wall of at least one of the N burners is the image, through a homothety and a rotation of 360xc2x0/N/n, of the general shape of the peripheral wall of at least one of its neighbours on said line, n being a whole number that is not zero. This arrangement can in particular permit improvement of the diffusion of the hot gases resulting from the combustion of the combustible mixture.